Computer models for electrical conductivity of multicomponent solid-state systems

Models for the computer simulation of electrical conductivity of polycrystalline materials and mixtures are proposed. The effect of model parameters on the concentration behavior of conductivity is considered. The correspondence between the model parameters and the characteristics of physical objects is established, thus making it possible to analyze the spatial relations in solid-state systems.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1868–1873, November, 1993.     

Surface solid-state interactions in copper-nickel-cement catalysts for hydrogenation of oxygen

The surface phase composition of alumocalcium cement-supported CuO and CuO-NiO catalysts prepared by chemical mixing has been studied using the method of thermo-vacuum curves of electric conductivity. The deactivation of these catalysts due to overheating to 800 °C under conditions of hydrogenation of oxygen is rationalized by the partial extraction of CuO (and NiO) from the stabilizing structure of the support solid solutions and by sintering of the extracted oxides and the reduced metallic phase. Complete regeneration of the CuO-NiO-talum catalysts can be achieved if a considerable amount (20%) of copper hydroxocarbonate is added.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1559–1562, September, 1994.     

Computer simulation analysis of conductivity of supported polydisperse systems

Effects of the support texture and the supported phase distribution on the conductivity of an individual grain or a granulated system have been analyzed theoretically. Experimental criteria are discussed, which allow one to judge the porous structure and sites of localization of a conducting component on the basis of the concentration dependence of the conductivity.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1449–1453, August, 1995.The authors are grateful to the International Science Foundation for partial financial support of this work (Project No. M 63000).     

Non-ohmic electrical conductivity of β-rhombohedral boron in high electric fields

The low-field conductivity of β-rhombohedral boron follows Mott's law of variable-range hopping. Recent improvements in the energy band scheme attribute the hopping centers to specific, partly occupied states in the band gap, evoked by structural defects, in particular unoccupied B(13) sites. Band type conductivity is also possible, after valence electrons have been excited into unoccupied gap states. An experimental tool to gain an insight into the transport mechanism of semiconductors is the field-dependence of the electrical conductivity. For the interpretation of such experiments various theories are at disposal: the classical model of hot electrons, the Poole-Frenkel model, models of non-thermally activated hopping by Mott and Shklovskii, the Model of the field-dependence of small polarons mobility, the model of space-charge-limited currents. New measurements of the electrical conductivity in the temperature range 187-303 K at field strength up to 8 k V cm⁻¹ are presented and discussed according to the above-mentioned theories together with a critical review of the previous measurements of other authors. Three ranges are to be distinguished. (i) Up to about 200 V cm⁻¹: ohmic behavior; (ii) between about 200 V cm⁻¹ and about 20 kV cm⁻¹: non-ohmic behavior with a temperature-dependent field-dependence; (iii) above the “electrical breakdown” at about 20 kV cm⁻¹: non-ohmic behavior with I:E² independent of temperature.     

Morphology and electric conductivity of cross-linked polyethylene–carbon black blends prepared by gelation/ crystallization from solutions

 Ultra-high-molecular-weight polyethylene (UHMWPE) – carbon black (CB) blends were prepared by gelation/ crystallization from PE dilute solutions containing CB particles. The UHMWPE/CB composition chosen were 1/0.15, 1/0.25, 1/0.5, 1/0.75, 1/1, 1/3, 1/5, and 1/9, etc. The cross-linking of PE chains was performed by chemical reaction of dicumyl-peroxide at 160 ^°C. X-ray diffraction patterns indicate that the crystallinity of PE within the blends decreased drastically through the chemical reaction at high temperature. The sample preparation method by gelation/crystallization provided the UHMWPE–CB system with various CB contents up to 90% and the conductivities for the resultant specimens were in the range from 10^-9 to 1 Ω^-1 cm^-1 corresponding to the electric conductivity range of semiconductors. The blends assured thermal stability of electric conductivity by cross-linking of PE chains, although the mechanical property such as the storage and loss moduli were very sensitive to temperature. The conductivity of the blends with CB content ≥20% were almost independent of temperature up to 220 ^°C and the values in the heating and cooling processes were almost the same. On the other hand, for the UHMWPE–CB blends with 13% CB content corresponding to the critical one, temperature dependence of electric resistivity showed positive temperature coefficient (PTC) effect. The PTC intensities for non-cross-linked and cross-linked materials were lower than that of the corresponding low-molecular-weight-polyethylene (LMWPE)–CB blend but the maximum peak appeared at 160 ^°C which is higher than the peak temperature of LMWPE–CB blend. Received: 10 December 1997 Accepted: 9 April 1998     

Modelling investigation on the thermal conductivity of pure liquid,vapour, and supercritical refrigerants and their mixtures by using Heyen EOS

This work presents a literature survey of the available data regarding the thermal conductivity of refrigerants. About 31 pure refrigerants that contain 7127 data points are selected for the temperature range of 91.35–580.00 K, a pressure range of (0.000111-500) bar, and thermal conductivity range of (0.007–0.27) W m^?1 K^?1 containing liquid, vapour, and supercritical phases. Seven binary and three ternary mixtures are also collected both in liquid and vapour phases with an overall of 803 data points. Based on the similarity between the pressure-volume-temperature and Tλ (thermal conductivity) P diagrams, the thermal conductivity model based on Heyen equation of state has been developed for pure refrigerants and their mixtures. The genetic algorithm is used to determine the adjustable parameters of the model. The calculation results prove that this proposed model can reproduce and predict thermal conductivity of refrigerants with good accuracy (overall AAD = 6.85% for pure compounds, AAD = 6.14% for binary mixtures and AAD = 9.32% for ternary mixtures).     

Evaluation of measurement uncertainty in analytical assays by means of Monte-Carlo simulation

The main limitations of the Guide to the expression of Uncertainty Measurement (GUM) approach for evaluating the measurement uncertainty of analytical assays are presented and explained. The advantages of using Monte-Carlo simulation against the GUM approach are outlined and discussed and the principle of propagation of distributions is explained. The procedure of Monte-Carlo analysis is illustrated by two case studies. A first simple example quoted from the EURACHEM Guide and dealing with the preparation of a calibration standard is used to present the technique with detail in a step-by-step way. In this case the results obtained by both approaches are very similar. A second example deals with the calibration of mass according to a strong non-linear model. In this case, the Monte-Carlo analysis leads to better results.     

The influence of particle shape and size on electric conductivity of metal-polymer composites

The effective electric conductivity of metal-polymer composite is investigated theoretically as a function of the electric conductivities of the constituents, of the particle shape and size and of the volume of loading. And, in order to consider the interaction between the metal particles, a self-consistent way is used to improve this function. Firstly, the percolation threshold decreases rapidly with increasing the metal particles axial ratio and decreasing the metal particle size. Secondly, the dependence of the metal particle shape and size on the effective electric conductivity of metal-polymer composite is investigated. Finally, the theoretical results on the effective electric conductivity of tin-polypropylene composite are in good agreement with the experimental data.     

Molecular simulation of the high-pressure phase equilibria of binary atomic fluid mixtures using the exponential-6 intermolecular potential

Molecular simulation results using the exponential-6 intermolecular potential are reported for the phase behaviour of the atomic binary mixtures of neon+xenon, helium+neon, helium+argon and helium+xenon. These binary mixtures exhibit both vapour–liquid and liquid–liquid phase equilibria up to very high pressures. Comparison with experiment indicates good overall agreement. The results indicate that the exponential-6 intermolecular potential is a useful generic potential for molecular simulation.     

The conductivity of dilute electrolyte solutions: Expanded lee and wheaton equation for symmetrical,unsymmetrical and mixed electrolytes

The conductivity equation of Lee and Wheaton is expanded in a power series in the ionic strength I. Different levels of approximation are analyzed and it is shown that for unsymmetrical electrolytes it is necessary to keep the terms I^3/2lnI and I² to maintain the performance of the full equation.     

Analysis of binary mixtures by computer decomposition of molecular fluorescence spectra

Qualitative analysis by computer decomposition of fluorescence spectra by means of the program SPECSOLV is discussed. Concentration studies of naphthacene in benzene and mixture analyses of single and binary solutions of anthracene, naphthacene, naphthalene,and rubrene are reported. The results demonstrate the ability to separate solvent and sample spectral contributions, and to assign component peaks in the case of mixtures. Semi-quantitative results are presented, and the feasibility of extending the study to computersearch systems based on component characterization of fluorescence spectra is discussed.     

Phase diagram and electrical conductivity of TbBr3-NaBr binary system

Several experimental techniques were used to characterise the physicochemical properties of the TbBr₃-NaBr system. The phase diagram determined by DSC, exhibits an eutectic and a Na₃TbBr₆ stoichiometric compound that decomposes peritectically (759 K) shortly after a solid-solid phase transition (745 K). The eutectic composition, x(TbBr₃)=39.5 mol%, was obtained from the Tamman method. This mixture melts at 699 K. With the corresponding enthalpy of about 16.1 kJ mol^-1. Diffuse reflectance spectra of the pure components and their solid mixtures (after homogenisation in the liquid state) confirmed the existence of new phase exhibiting its own spectral characteristics, which may be possibly related to the formation of Na₃TbBr₆ in this system. Additionally, the electrical conductivity of TbBr₃-NaBr liquid mixtures was measured down to temperatures below solidification over the whole composition range. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of flavonoids by CE using capacitively coupled contactless conductivity detection

A CE method employing capacitively coupled contactless conductivity (C(4)D) compared to indirect UV-detection was developed for the analysis of phytochemically relevant flavonoids, such as 6-hydroxyflavone, biochanin A, hesperetin and naringenin. To ensure fast separation at highest selectivity, sensitivity and peak symmetry, the pH value and the concentration of the running BGE had to be optimized regarding both co- and counter-EOF mode. Optimum conditions were found to be 1.0 and 5.0 mM chromate BGE (pH 9.50) in the counter- and co-EOF mode, respectively. Validation of the established CE-C(4)D method pointed out to be approximately seven times more sensitive compared to indirect UV-detection applying the same conditions. The lower LOD defined at an S/N of 3:1 was found between 0.12 and 0.21 microg/mL for the analytes of interest using C(4)D and between 0.77 and 1.20 microg/mL using indirect UV-detection. Compared to an earlier published CE method employing direct UV-detection, C(4)D was found to be approximately two times more sensitive. Due to the lower baseline noise, C(4)D showed an excellent regression coefficient >0.99 compared to 0.93 when using indirect UV detection calibrating within a concentration range between 1 and 10 microg/mL. The influence of the sugar moiety on the conductivity of a flavonoid was studied upon the analysis of the aglycon hesperetin and the rutinosid hesperidin. The sugar moiety in hesperedin shows a higher conductivity compared to hesperetin. Finally, the optimized established CE-C(4)D method was applied to the determination and quantification of naringenin in Sinupret.     

密度泛函理论模拟外电场对铁氧体电子结构的影响

通过密度泛函理论(DFT)模拟了3种典型的铁氧体(Fe₂O₃、Fe₃O₄和α-FeOOH)受外电场作用下的电子结构，研究了外电场对不同铁氧体电子结构的影响。DFT模拟结果显示：外电场的存在能够有效提高Fe₂O₃、Fe₃O₄和α-FeOOH晶体结构的价带位置，从而导致3种铁氧体的带隙出现明显的降低；当外电场强度为0.01 V·nm^-1时，Fe₂O₃、Fe₃O₄和α-FeOOH的带隙分别降低了0.36、0.12和0.34 eV；当电场增大至0.1 V·nm^-1时，Fe₂O₃晶体出现击穿现象，Fe—O化学键断裂导致Fe原子的电子沿外电场方向高度离域至相邻Fe原子，而Fe₃O₄和α-FeOOH则仅出现不同价带能级电子局域性增强且能量同质化，因而显示出相对稳定的物理化学结构。此外，外电场的存在可导致3种铁氧体价带电子均出现简并现象，且随电场强度增大而增强。3种铁氧体中，外电场的存在导致Fe₂O₃晶体中Fe原子的电荷密度增大而降低O原子的电荷密度； Fe₃O₄晶体结构中不同配位结构的Fe原子以及配位O原子的Hirshfeld电荷几乎不受外电场的影响； α-FeOOH晶体中共边FeO₆配位结构的Hirshfeld电荷受外电场影响较小，而共角FeO₆配位结构的Hirshfeld电荷受外电场影响较大，且H原子的电荷在强外电场作用下发生歧化响应。随着外电场强度逐渐增大，Fe₃O₄晶体的电子自旋态密度逐渐增大，而α-FeOOH晶体的电子自旋态密度则显示出降低的规律。     

密度泛函理论模拟外电场对铁氧体电子结构的影响

通过密度泛函理论(DFT)模拟了3种典型的铁氧体(Fe₂O₃、Fe₃O₄和α-FeOOH)受外电场作用下的电子结构,研究了外电场对不同铁氧体电子结构的影响。DFT模拟结果显示:外电场的存在能够有效提高Fe₂O₃、Fe₃O₄和α-FeOOH晶体结构的价带位置,从而导致3种铁氧体的带隙出现明显的降低;当外电场强度为0.01 V·nm^-1时,Fe₂O₃、Fe₃O₄和α-FeOOH的带隙分别降低了0.36、0.12和0.34 eV;当电场增大至0.1 V·nm^-1时,Fe₂O₃晶体出现击穿现象,Fe—O化学键断裂导致Fe原子的电子沿外电场方向高度离域至相邻Fe原子,而Fe₃O₄和α-FeOOH则仅出现不同...     

Impedance modelling of two-phase solid-state ionic conductors. Part I—theoretical model and computer simulations

An equivalent circuit model is introduced to account for the impedance properties of solid state ionic conductors, composed of two distinct phases. The model is developed on the basis of physical arguments, regarding the micrometer-scale structure of the two-phase material system and the comparison of different possible equivalent circuit representations. The final equivalent circuit reduces to two simpler circuits, suitable for fitting experimental impedance spectra. Computer simulations are provided to demonstrate the non-Arrhenius behaviour, which is observed in the temperature dependence of the ohmic elements of the equivalent circuits used for data analysis. This complex dual-slope behaviour of the Arrhenius plot is in agreement with the predictions of the model. Finally, with the aid of mathematical calculations and illustrated by computer simulations, a modified Arrhenius plot evaluation procedure was developed to derive correctly the electrical properties of the individual constituent phases from impedance measurements.     

Symposium overview computer simulation of inorganic solids

Summary A symposium on Computer Simulation of Inorganic Solids, organised by the Applied Solid State Chemistry Group Trust and by the Polar Solids Group of the Royal Society of Chemistry was held in London, in December 1988. Speakers at the forefront of research in computational techniques for simulation of inorganic solid materials reviewed the range of application of these methods and the prospects for future application to a largely non-specialist audience.The meeting was timely and well supported. The majority of the talks given are presented in this volume. This overview discusses the recent expansion of interest in solid state chemistry and the important role that computer simulation methods have played in this growth. The papers are summarised with especial reference to recent developments in solid state chemistry and materials science.     

Effects of non-additive conductivity variation for a nematic liquid crystal caused by magnetite and carbon nanotubes at various scales

Effect of magnetite and single-walled carbon nanotubes (CNTs) on the electric conductivity of 6CHBT nematic liquid crystal (LC) dispersed in polyvinyl alcohol is studied. The chosen technology of mixture homogeneising is shown to result in a LC dispersed in a polymer matrix (PDLC) with average LC droplet size of 500 nm (nano-PDLC). The conductivity of the nano-PDLC films with simultaneously introduced magnetite and nanotubes is shown to be smaller than the sum of the conductivities of films with nanoparticles of each type introduced separately. The main reason for this effect is assumed to be the formation of deep electron trap levels from complexes of nanoparticles of different type and thereby a decrease of the electron conductivity across the polymer which is the main mechanism of charge transfer in nano-PDLC. The effect of magnetite and the CNTs on the conductivity of the homogeneous LC and the micro-PDLC is analysed in comparison with the nano-PDLC.     

Analysis of anesthetic gas mixtures of halothane,nitrous oxide and oxygen by gas chromatography

Summary A simple dual-column system with a thermal conductivity detector is described, that can be used for the quantitative analysis of anesthetic gas mixtures of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane), nitrous oxide and oxygen. The separation was performed on a Carbopack (SP 1000) column and a Porapak Q column arranged in series across the detector.